Human immunodeficiency virus type 1 (HIV-1) is the causative agent of AIDS in humans. Dendritic cells (DCs) are one of the initial cell types that are targeted by the virus early following virus transmission to a naive host, and play a critical role in the establishment of productive virus infection and dissemination of HIV-1 in vivo. While DCs themselves are invariably infected, HIV-1 particles captured by DCs are efficiently transmitted to CD4+ T cells, a mechanism of HIV-1 trans infection. Though studied extensively, the mechanisms by which HIV-1 particles invade DCs have remained elusive. A number of dendritic cell-specific HIV-1 attachment factors have been proposed to account for DC-mediated virus capture in a HIV-1 envelope glycoprotein gp120 dependent manner. But targeted neutralization of any or all of these previously proposed HIV-1 attachment factors in DCs, fails to inhibit virus capture or transmission of captured HIV-1 particles from DCs to T cells, suggesting the existence of gp120-independent virus capture mechanism(s) in DCs that is crucial for the establishment of HIV-1 trans infection. We propose that HIV-1 can bind DCs using glycosphingolipids expressed in the lipid bilayer of the virus particle membrane and that these virus particles bound independently of gp120 can be transmitted to CD4+ T cells. The goal of this project is to identify the nature of the HIV-1 gp120-independent, glycosphingolipid-dependent mechanism of binding to DCs. We will attempt to identify the glycosphingolipids on the HIV-1 particle surface that mediate attachment to DCs using two independent experimental strategies. We will utilize a targeted siRNA-based approach to selectively deplete GSLs in the virus-producer levels to determine the class of GSLs necessary for virus particle attachment to DCs. We will next use comparative mass spectrometry based lipidomics strategy to identify the specific GSL that mediates virus particle attachment. Finally, we will determine if GSLs present in the virus particle membrane are crucial for targeting HIV-1 particles to the DC-mediated T cell trans infection pathway. Understanding the mechanism by which this occurs will provide information about a key step in the HIV - dendritic cell interaction pathway, and provide insights into the role of dendritic cells in HIV-1 pathogenesis. Furthermore, elucidation of this mechanism of HIV-1 attachment to DCs might provide novel targets for design of anti-virals that specifically target an early step in the HIV-1 life cycle. PUBLIC HEALTH RELEVANCE: The aim of this project is to identify the mechanism(s) by which human immunodeficiency virus type 1 (HIV-1) can bind dendritic cells, a critical step in the establishment of infection and dissemination of virus in vivo. A detailed understanding of this crucial step in HIV-1 pathogenesis could lead to the development of anti-virals such as microbicides that prevent transmission of HIV-1 to a naive host.